• Book by WhatsApp first (634 74 27 68): visits are timed guided tours with limited space, and busy seasons sell out
• Up a flight of stairs, no elevator: the museum is on the first floor of a shopping arcade, and strollers stay parked where the guide says
• Bring a letter from home: Ratón Pérez has his own mailbox inside, and posting to it is part of the visit

Spain's tooth fairy is a mouse, Ratón Pérez, and in Luis Coloma's story for the boy king Alfonso XIII he lives in a cookie tin at Calle Arenal 8. This small museum on that spot shows his family home inside a giant Huntley cookie tin, the mailbox where kids post him letters, and scenes from the tale of King Bubi's first lost tooth, all on a guided tour.